Serum amyloid P component and autoimmune parameters in the assessment of arthritis activity in MRL/lpr/lpr mice

The concentration of immunoglobulins, anti-ssDNA, anti-dsDNA, anti-TNP antibodies, IgM rheumatoid factor, C3, immune complexes and serum amyloid P component (SAP), in the serum were measured in 68 male and female MRL/lpr/lpr mice, a strain affected with a systemic autoimmune disease. The degree of lymphoproliferation was assessed by the spleen weight. Spontaneous secretion of immunoglobulins and anti dsDNA antibodies were measured in spleen cell cultures. All mice presented age related increases or decreases (C3) in the level of measured parameters. Inflammatory lesions were detected, by light microscopy in the joints of all mice. There was a significant correlation, in both sexes between the serum level of SAP and the severity of the polyarthritis, as assessed by light microscopy. In female mice the levels of anti-dsDNA antibodies, immunoglobulins, either measured in serum or in the spleen compartment, and circulating immune complexes also showed correlation with the activity of the arthritis, but neither of these variables correlated as closely with arthritis scores as did serum SAP.